A disk drive is a data storage device that stores digital data in concentric tracks on a data storage disk. During disk drive operation, the disk is rotated about an axis by a spindle motor while a transducer (head) reads data from and writes data to a target track of the disk. A servo controller uses servo data read from the disk to position the transducer above the target track while the data transfer takes place.
When the transducer moves off-track during a write operation, the transducer might inadvertently write data on or near an adjacent track (squeeze), thus corrupting data on the adjacent track (encroachment). In addition, data that is written off-track by the transducer may be difficult or impossible to read from the target track due to its off-track position. As a result, side track erasure can increase bit error rate (BER) and data loss.
Side track erasure is traditionally addressed by transducer design. However, as transducers operate with higher write magnetization, side track erasure is increasingly difficult to avoid. Furthermore, transducers and disk drives that exhibit errors due to side track erasure are failed and discarded or returned, thereby lowering manufacturing yield and increasing cost.
There is, therefore, a need to detect side track erasure, to minimize side track erasure before user data is harmed, and to reduce failed transducers and disk drives due to side track erasure.